3. Normal Hemostasis
• Normal Hemostasis:
• Maintain blood in fluid form, clot free
• Formation of plug at site of injury
• Prevention of blood loss
• Sequence of events after injury
• Transient arteriolar vasoconstriction
• due to neurogenic reflex & endothelin secretion.
• Primary hemostasis:
• Endothelial injury exposes sub-endothelial
thrombogenic extra-cellular matrix ECM → facilitate
platelets adherence, activation, shape change, release
of granules and aggregation→plug formation in minutes
4. Normal Hemostasis
• Secondary hemostasis:
• Endothelium releases tissue factor (III or Thromboplastin)
• tissue factor III and Factor VII → activate coagulation
cascade → thrombin → fibrinogen → fibrin → polymerized
→ fibrin mesh → cementing platelets into solid plug
• Thrombin → more platelets.
• Counter-regulatory mechanisms
• tissue Plasminogen Activator (t-PA) come into action to
limit the process by fibrinolysis
5.
6. Hemostasis and Thrombosis
• Normal Hemostasis:
• Maintenance of blood in fluid form, clot free,
with formation of hemostatic plug at site of
vascular injury to prevent blood loss.
• Thrombosis:
• “An inappropriate activation of normal
hemostatic processes with formation of blood
clot (thrombus) in intact vessels or thrombotic
occlusion of vessel after minor injury”
9. Hemostasis & Thrombosis
I. Normal endothelium
• Antithrombotic properties
• Inhibitory effects on platelet:
• Intact endothelium prevents platelet from meeting
thrombogenic ECM and adherence. Endothelium stimulated
by cytokines and thrombin release Prostacyclin (PGI2) & nitric
oxide which inhibit platelet adhesion and aggregation.
ADPase prevent aggregation
• Inhibitory effects on coagulantion factors:
• Prevents activation of coagulation cascade by producing
heparin-like molecules (inactivate thrombin),
Thrombomodulin (activates proteins C and S anticoagulants
synthesized by endothelium) and tissue factor
• Fibrinolytic properties:
• Synthesize tissue Plasminogen Activator t-PA
10. Hemostasis & Thrombosis
I. Normal endothelium
• Prothrombotic properties of Injured / activated
Endothelium
• Endothelium is activated by Infectious agents,
Hemodynamic disturbances and Plasma mediators
• Induced by cytokines (TNF, IL1) & bacterial endotoxin →
release of tissue factor → activates extrinsic pathway of
coagulation
• Endothelial injury exposes subendothelial ECM containing
von Willibrand factor (vWF) attached to collagen that binds
to Gp1b on platelets → their adherence
• Endothelial releases Inhibitors of Plasminogen activators
(PAIs) → depress fibrinolysis
11. 2. Platelets
• Anucleate, non-adherent discs,
• has Integrin family glycoprotein
Receptors, ontractile cytoskeleton and
2 types of granules
• α granules ( P-selectin) contain fibrinogen, fibronectin,
factor V and VII, Platelet factor 4, PDGF, TGF-β)
• δ granules (ATP & ADP, Ca, histamine, epinephrine)
After vascular injury, platelet contact with ECM → 3
changes.
• Adhesion , activation and aggregation.
• Adhesion: vWF platelet glycoprotein interaction →
extended shape of vW factor, acting as bridge between
platelets and collagen.
12. II. Platelets
• Activation: Shape change and release of granules -
ADP activates Platelets. Shape change to spheres
with spiky extensions. Secrete calcium and
Thromboxane TxA2. negatively charged surface
phospholipids bind ca and clotting facors .. sticky
platelets →
• Aggregation: is stimulated by thromboxane. surface
glycoprotein binding to fibrinogen promote
aggregation. Coagulation cascade activated by Ca++
→ hemostatic plug. Thrombin activates protease
activated receptor PAR on platelet which along with
ADP and TxA2 enhances aggregation. It also convert
Fibrinogen to fibrin that cement the platelet plug.
13. III. Coagulation Cascade
• Damage to blood vessels
• 1. Intrinsic Pathway: begins with
• Imp. coagulation factor--Hageman factor XII.
• 2.Extrinsic pathway: begins with tissue injury
and tissue factor and factor VII.
• Conversion of Prothrombin to Thrombin
• Conversion of fibrinogen to fibrin to form clot.
14.
15. Coagulation cascade
• Thrombin
1. converts fibrinogen to fibrin
2. causes platelets activation/aggregation
3. induces endothelium to produce adhesion
molecules
4. activates monocytes
• Anti-thrombosis by natural Anticoagulants ie
Anti-thrombin III, Protein C and S
• Fibrinolytic cascade: plasminogen activated by
urokinase, t-PA and streptokinase → plasmin →
break down of fibrin
16. THROMBOSIS
“An inappropriate activation of normal
haemostatic processes,
such as formation of thrombus in an
uninjured vasculature
or thrombotic occlusion of a vessel after
minor injury”.
Attached to vessel wall
17. Causes of thrombosis
VIRCHOW’S TRIAD: Three principle abnormalities
THROMBOSIS
Endothelial injury
Blood
Hypercoagulability
Abnormal
Blood Flow stasis
/ turbulence
18. 1. Endothelial injury
• Exposure of sub endothelial collagen
• Adhesion of platelets
• Production of tissue factors and PAI
• Local depletion of t-PA, Prostacyclins PGI2,
• Examples:
• Myocardial Infarction, valvulitis ulcerated plaques over
atheroclerosis, Vasculitis due to injury and
inflammation, Injury due to hypertension, scarred
valves or bacterial endotoxins, Homocystinuria,
Hypercholesterolemia, Radiation, chemicals in cigarette
smoke.
19. 2. Abnormal Blood flow
• Mechanism:
• Turbulence in cardiac and arterial thrombi
• Stasis in veins
• Disruption of laminar flow - platelets and leucocytes get more
contact time with endothelium .
• Promote endothelial cell activity, Enhanced pro-coagulant
activity
• Slow washout of activated clotting factors
• Impeded inflow of clotting factor inhibitors
• Examples
Ulcerated Atherosclerotic plaques, Scarred valves
Aneurysm, Myocardial Infarction, Mitral valve stenosis in
Rheumatic Heart Disease, Atrial fibrillation, Hyper viscosity
syndromes (polycythemia), Sickle cell disease
20. 3. Hypercoagulability
• Any alterations of the coagulation pathways that
predisposes to thrombosis.
• Primary (Genetic) disorders
• Inherited deficiency of anticoagulants (factor C, protein
S, anti thrombin III)
• Elevated levels of Homocystein
• Mutations in factor V and prothrombin genes
22. Heparin Induced Thrombocytopenia
Syndrome
• administration of unfractionated heparin for
anticoagulation.
• induces circulating autoantibodies that bind to
complexes of platelet factor 4 & heparin, on
endothelium and platelets
• →platelet activation, aggregation or consumption
and endothelial injury – prothrombotic state
23. Anti-phospholipid antibody syndrome
• Cluster of protean manifestations including recurrent
thrombosis, repeated miscarriages, cardiac valve
vegetations and thrombocytopenia
• associated with serum autoantibodies against anionic
phospholipids (cardiolipins)
• antibodies in vivo induce hypercoagulable state by
platelet or complement activation and endothelial
injury
• In vitro interfere with phospholipid assembly and
inhibit coagulation
• Occur as primary disease or Secondary to autoimmune
disease SLE
24. Morphology Of Thrombi
Sites: Anywhere in CVS. cardiac chambers, valve cusps,
arteries, Veins and capillaries.
Size and shape: variable, depend on site and
circumstances.
Adherent to underlying vessel or heart wall.
propagating portion poorly attached, prone to fragment
and migrate as embolus
Lines of Zahn: Gross and microscopic laminations.
Represent pale platelet and fibrin layers alternating
with darker red cell rich layers. Formed in flowing
blood, distinguish from postmortem clotting.
25. Cardiac or mural and Arterial thrombi
At site of endothelial injury or turbulence
Due to abnormal myocardial contraction
Vegetations or Thrombi on cardiac valves can be:
infective -Infective endocarditis
Non-infective (NBTE) - debilitated patients with
hypercoagulable states, Libman-Sacks endocarditis
immune mediated (in SLE)
Tend to grow in retrograde direction from point of
attachment. Relatively rich in platelets
Arterial thrombi are usually occlusive, superimposed
upon atherosclerotic plaque. Most common - coronary,
cerebral, femoral
26. Dark red thrombosis within lumen of coronary artery.
Gross Morphology: grey red, friable, laminations called
lines of Zahn alternating pale layers of platelets & fibrin
and dark layers of RBCs
27. Main pulmonary trunk and pulmonary arteries showing
a large "saddle" pulmonary thromboembolus.
29. Microscopic morphology of arterial thrombi: composed
of tangled mesh of platelets, fibrin, RBCs,& degenerating
WBCs. "Lines of Zahn" - alternating pale pink bands of
platelets with fibrin and red bands of RBC's
30. Phlebothrombosis Or Venous Thrombi
Occurs at site of stasis and is red
Lower and upper extremities, 90% lower limbs, peri-
prostatic, or ovarian, peri-uterine veins
almost occlusive. Extends in direction of blood flow i.e.
towards heart, often creates a long cast of venous
lumen.
Prone to fragment and create embolus
Microscopically: contains more enmeshed RBCs.
Laminations are not very apparent.
Postmortem clot
Intravascular clot formation after death of person due
to blood stasis
gelatinous, not adherent to vessel wall, dark red
dependant portion and supernatant chicken fat
appearance
31. Red or Venous
thrombi
Firm
Uniformly red
No supernatant
extremities
Have point of
attachment
Post mortem clot
Gelatinous
Dark red
Yellow supernatant
portion
dependent portion
Not attached to vessel
wall
33. Fate of thrombi
1. Propagation: enlargement of thrombus leading to
vessel obstruction.
2. Embolization: Dislodge, fragments travel to other sites.
3. Dissolution: by fibrinolytic pathway (usually in recent
thrombi), shrinkage and dissolution. Older thrombus
become resistant due to fibrin polymerization
4. Organization & Recanalization: in-growth of
endothelial cells, smooth muscles and fibroblasts into
fibrin rich thrombus (usually in old thrombi).
Formation of capillary channels reestablishing blood
flow. Further recanalization lead to formation of
vascularized connective tissue mass that into vessel
wall. Enzymatic digestion occurs due to Leucocyte
lysosomes. Superadded bacterial infection can weaken
vessel wall predispose it to aneurysm.
38. Clinical Correlations
Thrombosis is unpredictable, asymptomatic or
symptomatic, occur in both healthy or due to underlying
abnormality.
1. Venous and arterial obstruction.
2. Embolization:
3. Arterial thrombi are associated with
Dyskinetic myocardial contraction
Rheumatic heart disease can lead to Mitral
stenosis, stasis and thrombosis.
Atherosclerosis can cause abnormal blood flow
and loss of endothelial integrity.
Embolization to brain, kidney & spleen.
39. Clinical Correlations
4. Venous thrombi (Phlebothrombosis)
Embolization to lungs and systemic circulation
→ venous obstruction → Congestion, edema,
tissue infarction and death. Vericose ulcers,
Thrombophlebitis: inflammation associated
with thrombosis
i. Superficial thrombi (decreased risks).
Saphenous vein
ii. Deep vein thromboses (DVT) (increased risks
esp. over 50 yrs age). Femoral, popliteal, iliac
veins. asymptomatic, pain, edma. Migratory
thrombophlebitis in cancer or Trousseau
syndrome.
40. Disseminated Intravascular coagulation DIC
• “Sudden and insidious onset of widespread thromboses
within microcirculation”.
• activation of coagulation system through endothelial injury /
or release of thromboplastic substances into circulation.
• Occurs in severe infections, trauma, neoplasia and obstetric
complications.
• Potential complication of any condition associated with it:
1. widespread activation of thrombin. Small fibrin thrombi form
in small arteries of brain, heart, lungs, kidneys and other
organs to produce ischemic tissue damage.
2. Can lead to circulatory insufficiency.
3. Leads to consumption of platelets & coagulation proteins i.e.,
consumption coagulopathy.
4. Fibrinolytic mechanisms are activated leading to serious
bleeding disorders.
42. Thromboembolism
• Thrombosis is the formation of blood clot
within un-injured vessel or thrombotic
occlusion of vessel after minor injury.
• Embolus is a detached thrombus/any other
solid,liquid or gaseous mass carried by the
blood to a site away from its point of origin.
